Ores and other minerals, when mixed, usually contain various impurities, i.e., the desired mineral species usually occurs in admixture with other minerals. Thus, the desired mineral or ore usually must be separated from the rest of the material as mined.
Talc, for example, occurs in nature in rock formations in which it is typically associated with other minerals, such as dolomite, chorite, quartz, pyrite, magnesite, calcite, feldspar, mica, or mixtures thereof. For ease of description, as used in this application, "dolomite" shall be taken to mean dolomite and/or the aforementioned other minerals with which talc shall be admixed or otherwise associated in nature. A run-of-mine ore is generally composed, for the most part, of rocks of predominately one mineral species, e.g., talc rocks are admixed with dolomite rocks or the like. A very small percentage of conglomerate rocks containing varying mixtures of mineral species, such as talc combined with dolomite in the same rock, may be present as well.
Talc is commonly separated from other minerals, for example, dolomite, by manual sorting or flotation processes. Manual or hand sorting relies upon visual differences between the mineral species such as color variations, degree of granulation, size of the material lumps and the like which are perceptible to the persons doing the sorting. Manual sorting is, obviously labor intensive. It can also give rise to disabling injuries, including carpal tunnel syndrome. Flotation processes are capital intensive, chiefly due to the very expensive equipment necessary to carry them out. Furthermore, vast quantities of water are needed, water that is not available in many mining regions such as ones located in Montana and Australia.
Numerous attempts have ben made to develop automated sorting processes for sorting mineral species. Among these are optical sorting, which relies upon optical sensor-perceptible visual differences in light reflection from the surfaces of the ores or minerals to be separated, sink-float processes, which rely upon specific gravity differences in the materials being separated, and electrostatic separation methods based either on electrophoresis or dielectrophoresis, which relies upon the differences in conductivity or shape of the mixture's components. None of these automated sorting processes, however, have been completely successful in that they can be affected by color variations between the particles, shape variations, specific gravity differences and mineral size variations, to name just a few factors.
A number of automated sorting processes based on particle shape have been developed. For example, the separation of coal from its associated rock is shown in U.S. Pat. Nos. 1,030,042 issued June 18, 1912 to Wilmot et al. and 1,190,926, issued July 11, 1916 to Lotozky. Coal suitable for separation by these patented processes is granular in form and generally of a more or less spherical configuration. The associated rock, which includes slate, must on the other hand be present in the form of more or less flat shaped pieces.
In the Wilmot et al. process a mixture of coal and its associated rock is placed in a chute having a rotating disc halfway down its length. The coal, being generally spherical in shape, rolls down the chute and comes to rest in a bin at the bottom of the chute. The associated, generally flat rock slides down the chute until it reaches the rotating disc, where it comes to rest and is carried away from the chute by the disc.
In the Lotozky process a chute is not used. Instead, a mixture of coal and rock is fed onto the surface of an inclined rotating disc in a direction opposite to that in which the disc is moving. The coal, which is again generally spherical in shape, continues to roll down the disc in its original direction. The flat rock comes to rest on the disc and is carried away.
These separation processes rely upon the shape of the particles to be separated, in particular the extent to which the particles being separated are or are not spherical, thus utilizing both rolling and sliding coefficients of friction in the sorting process rather than differences between the sliding coefficients of friction of the two types of particles being separated. Furthermore, Wilmot et al.'s and Lotozky's rotating discs are used solely to physically carry slate or other flat rocks out of the slate/coal stream, not to impart centrifugal acceleration to separate coal from the other materials present.
Other automated sorting methods and apparatus based solely on particle shape include, for example, those disclosed in U.S. Pat. No. 4,059,189, issued Nov. 22, 1977 to John. The separation of particles with identical composition but different shape is again based on the degree of sphericity of the particles being separated as demonstrated by their differences in rolling and sliding coefficients of friction. Yet another automated apparatus for separating particles based upon their degree of sphericity is shown in U.S. Pat. No. 3,485,360, issued Dec. 23, 1969 to Deinken et al. The Deinken et al. apparatus consists of a rotating disc to which a mixture containing generally spherical and irregularly shaped, generally nonspherical particles of identical composition is fed. The spherical particles roll off the disc, while irregularly shaped particles are forcibly removed from the surface of the disc. Another automated separation process, that disclosed in U.S. Pat. No. 1,744,967, issued Jan. 28, 1930 to Johnson, requires the application of an electrostatic field. The Johnson process operates on a frictional difference obtained chiefly by increasing gravitational force by applying an electrostatic force to take advantage of the fact that flat particles create a stronger electrostatic field than spherical particles.
Automated sorting processes have also been developed to separate particles by differences in their adhesive properties; see U.S. Pat. No. 3,508,645, issued Apr. 28, 1970 to Conrad. In the Conrad process sticky particles, such as chicken meat, are made to adhere to a moving surface by static bonding while nonsticky particles, such as associated chicken bones, slide off the moving surface.
Other separation processes have been used to separate material mixtures by gravity concentration using the density differences between the mixture components. These processes may be carried out on ore concentrating tables, a form of a vibratory table.
None of the above-mentioned automated sorting processes separate different mineral species by taking advantage of differences in sliding coefficients of friction exhibited by the mineral species being separated.
It has now been discovered that the constituents of mixtures of discrete particulate materials, e.g., a mixture of two or more granular or rocklike mineral materials of dissimilar chemical constitution but similar physical configuration, can be separated one from another by a novel sorting technique that utilizes differences in the sliding coefficients of friction of the materials being separated, thus obviating the need to form such materials into different shapes to effect separation thereof.
It is, therefore, an object of this invention to provide methods and apparatus for separating different materials, including, but not limited to, different minerals having different sliding coefficients of friction by taking advantage of such sliding coefficient of friction differences.
It is also an object of this invention to provide methods and apparatus for the separation of talc from associated minerals and rocks utilizing the differences in the sliding coefficients of friction exhibited by talc and such associated mineral species to produce high-grade talc products and upgraded talc mixtures.
These and other objects, as well as the nature, scope and utilization of the invention will become readily apparent to those skilled in the art from the following description, the drawings and the appended claims.